Patent Literature 1 discloses, in an attempt to improve the bioavailability of the active ingredient, a “pharmaceutical composition with a bioavailability of the active substance which is substantially independent of the gastric pH, for oral administration of active substances with pH-dependent solubilities and a dose number of more than 1 at a pH>5, comprising a plurality of pellets synthesized in each case from a) a core material, b) an optional insulating layer, c) an active substance layer and d) an optional coating, wherein the core material consists of one or more pharmaceutically acceptable organic acid(s) with a water solubility of more than 1 g/250 ml at 20° C., optionally with the addition of binders or other technological adjuvants.”
However, the reference does not describe pioglitazone and a salt thereof.    Patent Literature 1: JP 2005-526738 A